(a) Field of the Invention
This invention generally relates to a system for warning drivers of a vehicle of an approaching emergency vehicle, such as an ambulance, police car, or fire truck. More particularly, but not by way of limitation, to a device that detects the presence and approximate location of an approaching emergency vehicle and advises the driver or user on how to avoid the emergency vehicle.
(b) Known Art
Emergency vehicles, such as ambulances, police cars, or fire trucks, typically carry a loud siren and flashing lights to warn motorists and other people on the road that the emergency vehicle needs the right of way. Unfortunately, however, many private vehicles are well insulated and include stereo systems which can fill the interior of the vehicle with sound such that the siren of the emergency vehicle becomes inaudible to the driver of the private vehicle. Furthermore, today""s highways and streets often include many lanes. When an emergency vehicle is traveling down one of these multi-lane roadways, it is often very difficult for the driver of the private vehicle to determine the relationship of the emergency vehicle relative to the private vehicle, such that the driver of the private vehicle can make a clear decision as to what to do to safely yield the right of way to the emergency vehicle. For example, in certain situations it may be prudent to pull over to the right of the roadway, while in other situations, it may be safer to pull over to the center or left side of the roadway. In order to make the decision of what is the safest action in yielding the right of way, it is important to know the position and direction of advancement of the approaching emergency vehicle relative to the private vehicle.
Known devices used for warning of an approaching emergency vehicle often use electromagnetic or acoustic waves to allow the emergency vehicle to communicate with the private vehicle. For example, in U.S. Pat. No. 4,747,064 to Johnston, a device which uses an electromagnetic pulse and an acoustic pulse receiver. The Johnston device uses the sound waves to determine the speed of the approaching emergency vehicle, so that the time left until the vehicles meet can then be calculated. An important limitation of the Johnston device is that it only provides information as to how much time is left until the approaching emergency vehicle and the private vehicle meet. This leaves the driver of the private vehicle guessing as to the direction of approach of the emergency vehicle. Perhaps of more importance is that, without knowing the direction of approach, the Johnston system does not help the driver of the private vehicle in deciding the direction towards which he should pull over to yield the right of way to the oncoming emergency vehicle.
Another known solution at warning about an oncoming emergency vehicle is taught in U.S. Pat. No. 4,238,778 to Ohsumi. The Ohsumi device warns the driver of the private vehicle by way of an audible signal. The audible signal intensifies or increases in volume as the emergency vehicle approaches the private vehicle. Additionally, a system for reducing interfering sound signals within the private vehicle is also included. This system lowers the sound volume of devices such as the private vehicle""s radio, fan or other noisy device within the vehicle.
Still another approach at the problem associated with warning drivers of an approaching emergency vehicle is taught in U.S. Pat. No. 3,854,119 to Friedman et al. The Friedman device is tuned to a particular radio signal which is used as a communication link between the emergency vehicle and the private vehicle. Thus the Friedman approach, like other known approaches, boosts the ability of the emergency vehicle to warn the private vehicle of the proximity of the emergency vehicle, but does not help the driver of the private vehicle in deciding on which direction to move in order to yield the right of way to the emergency vehicle.
Thus, there remains a need for an emergency vehicle warning system that alerts drivers of private vehicles that an approaching emergency vehicle is in the area. Still further, there remains a need for an emergency vehicle warning system that allows the driver of the private vehicle to determine the direction of approach of the emergency vehicle as well as helping the driver of the private vehicle to determine the safest direction to pull over to yield the right of way to the approaching emergency vehicle.
It has been discovered that the problems left unanswered by known warning systems can be solved by providing an emergency vehicle warning system that provides the driver of a private vehicle with information on the direction of approach of the oncoming emergency vehicle as well as the direction that the driver should pull over to yield the right of way to the approaching emergency vehicle. The disclosed emergency vehicle warning system includes:
1) a receiver and a display panel mounted in the private vehicle, and at least two infrared receivers mounted on the private vehicle. The display panel mounted in the private vehicle including indicating devices that allow the driver of the private vehicle to know of the approaching emergency vehicle as well as the direction to move in order to yield the right of way to an approaching emergency vehicle; and
2) a warning signal emitting device mounted in the emergency vehicle, the warning signal emitting device providing signals that allow the components of the emergency vehicle warning system mounted in the private vehicle to know that the approaching vehicle is an emergency vehicle.
According to a highly preferred embodiment of the invention the system uses a set of infrared transmitters as well as a set of infrared receivers. The infrared transmitters will be used to determine the proximity of adjacent vehicles or obstacles in order to locate a path for driving the private vehicle in yielding the right of way to the emergency vehicle. The infrared receivers are used to gather the reflected signals that emanated from the transmitters. Also, the receivers will allow the system to respond to an identification signal sent by the emergency vehicle.
The identification signal sent by the emergency vehicle will prompt the system to activate and determine the direction of approach of the emergency vehicle and the relative speed to the approaching emergency vehicle. The direction of approach is determined by the difference in time at which each of the receivers detected a pulsed identification signal sent from the emergency vehicle. The speed will the be determined by using the Doppler shift to calculate the speed of the approaching emergency vehicle.
Another example of an emergency vehicle warning system taught herein is described below. This example uses radio frequency signals and an antenna arrangement that is mounted on the private vehicle to determine the direction of approach of the emergency vehicle. This example is as follows:
1.0 General Description
The Emergency Vehicle Warning System is a radio frequency (RF) based electronic system designed to alert motorists of the presence of a nearby emergency vehicle responding to an urgent situation. The emergency vehicle, using a specially designed transmitter, sends out a low power RF signal so that automobiles in the area equipped with a companion receiver can detect its presence.
The motorist is alerted by an audio tone when the transmission is detected by their receiver. The approximate direction of the emergency vehicle from the motorist is then visually displayed by illuminating one of eight circularly positioned light emitting diodes (LEDs) on the receiver. The maximum operating range for the system is approximately 500 feet. The equipment is intended to be operated without a license under Part 15 of the FCC rules.
2.0 Transmitter Discription
The transmitter operates on a fixed RE frequency in the UHF band. It is normally powered from the emergency vehicle""s battery, and begins transmitting as soon as it is energized. According to FCC rules, the transmitter may be operated continuously during the emergency condition. The transmitted signal consists of a one second message that is constantly repeated. The message comprises a 150 mS digital recognition code followed by a period of unmodulated carrier (CW). Using digital AM modulation, the recognition code uniquely identifies the transmission as part of the Emergency Vehicle Warning System. The CW portion of the transmission lasts for 850 ms, to permit the receiver to measure the direction of the transmitted signal. A digital microcontroller, located internal to the transmitter, generates the transmitted message.
3.0 Receiver/Antenna Description
The receiver is located in the motorists vehicle and operates together with a special direction finding antenna mounted on the roof. Interconnecting cables between the receiver and antenna are used to route the received signal output and control signal inputs. FIG. 9 is a block diagram of the receiver/antenna interface. Normally, when no emergency transmission is present, the receiver is constantly listening for the beginning of a transmission from the emergency vehicle. A digital microcontroller performs this function. During this period, the antenna is configured as an omni-directional monopole to permit equal reception from all directions.
After the AM recognition code is successfully detected, the antenna is configured for Y-direction measurement (front-back) and then for X-direction measurement (left-right) during the remainder of the one second transmission. A low frequency, square-wave tone signal is generated by the receiver to effectively produce AM modulation on the received CW carrier and enable directional information to be extracted from the emergency transmission. The antenna then reverts back to the message reception mode, repeating the cycle continuously.
Because the receiver/antenna system is designed to operate only with the expected signal format of the emergency transmitter, it essentially synchronizes itself with it. This minimizes false alarms and allows direction measurements to be performed only while a valid signal is present.
3.1 Antenna Description
The receiver antenna consists of a five element Adcock array. Two elements are used for X-directional measurement, two for Y-directional measurement and one for xe2x80x9csensexe2x80x9d measurement. The sense antenna, located in the center of the array, is used for omni-directional message reception and to resolve the 1800 ambiguity that would otherwise result during direction measurement. The antenna system operates under control of the receiver, via interconnecting cables.
While the receiver is listening for a valid recognition code, the TONE input is disabled, effectively disabling the multiplier. Under this condition, RF signals from the sense antenna only are fed to the receiver. During Y-direction measurement, the X-Y control input configures the RF switches to select the front and back antennas, forming a Y-axis dipole antenna pattern. While the Y-axis antennas are selected, a 1 KHz square wave TONE signal is generated which in turn produces a double-sideband suppressed carrier AM signal at the output of the multiplier. The output of the sense antenna is added in quadrature to produce a conventional AM modulated signal. The percentage and polarity of the AM signal are directly related to the direction of the incident RF signal from the emergency transmitter. Alternately, when the polarity of the X-Y control signal is reversed, the left and right antennas are selected, permitting direction finding in the X-axis.
4.0 Receiver Description
A single frequency, superhetrodyne AM receiver is used. It processes recognition decoding and direction finding signals using the same circuitry. An integrated circuit microcontroller performs the timing, control, and direction processing functions.
Automatic gain control (AGC) of the iF stages is necessary to maintain the amplitude linearity required to properly demodulate the AM signals over wide input signal variations. The choice of AGC time constant is a compromise between response time and signal distortion. A fast acting AGO is desirable in order to track rapidly changing RF signal levels. However, if the response time is too quick, the desired AM signals will be xe2x80x9ctracked outxe2x80x9d, causing loss of information. A response time of approximately 50 ms is a reasonable compromise.
As mentioned earlier, the receiver""s microcontroller is designed to detect and demodulate the emergency transmitter signal. In the absence of an input signal, the receiver is constantly examining the AM detector output for the presence of a start bit, indicating the beginning of a valid transmission. When the recognition code has been successfully received, the direction finding processing begins. Then, the audio alarm is activated and the appropriate LED is illuminated to indicate the approximate direction of the emergency vehicle from the motorist. At the end of each message, the audio and LED indications are turned off until the next repeated message is processed. In this manner the audio beeps and the LED blinks. FIG. 12 describes the sequence of events during the processing of each transmission.
An analog to digital converter (A/D) in the receiver microcontroller measures the detected AM voltages during the OW portion of the transmitted message and performs the averaging and signal level comparisons necessary to predict the approximate direction of the emergency transmitter. One of the eight possible LEDs will be lit as a result of this measurement.
The results of the direction finding measurements can be summarized in a table that indicates how one of the eight LEDs is illuminated as a function of the X and Y AM levels and polarities. FIG. 14 illustrates such a table.
It should also be understood that while the above and other advantages and results of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings, showing the contemplated novel construction, combinations and elements as herein described, and more particularly defined by the appended claims, it should be clearly understood that changes in the precise embodiments of the herein disclosed invention are meant to be included within the scope of the claims, except insofar as they may be precluded by the prior art.